Smart cards have long been used for example as bank cards, identity cards and telephone cards or the like. On account of the further increasing number of possibilities for application of such smart cards and the associated increasing number of smart cards used daily by each user, aspects concerning recognition, differentiability of the cards of different providers or their functions and, associated therewith, safety in the use of the smart card are becoming more and more important.
In this case, in every day dealings the user has already become accustomed to the fact that the body of the smart cards is produced from varicolored plastic that is fashioned for example in a color that identifies the company that issues the respective card, and additionally bears for example the name of the company as lettering or a logo.
This colored configuration of the smart card body co-ordinated with the company affords the possibility of rapidly recognizing a specific smart card among other smart cards. However, it consists of conventional plastics, can easily be counterfeited and offers no security whatsoever that the smart card module integrated into the smart card also actually originates from the company mentioned on the smart card.
In order to ensure universal application of the smart cards, standards that determine the dimensions and technical details of the smart cards have been defined. Such standards are for example ISO 7810, relating to formats for identity documents, and ISO 7816, relating to identity cards with a contactless chip, so-called smart cards, and chips with contacts.
Depending on the field of use, smart cards are offered in a variety of variants, namely as the contactless smart cards already mentioned above, as smart cards “with contacts” and as combination cards. Here the last two in each case comprise a contact region, in which contacts corresponding to the specifications of the standard ISO 7816-2 in terms of their arrangement are provided. By means of said contacts, a circuit integrated in the smart card can be contacted externally, e.g. when data are read out in a specific reader. Said contacts are produced from a metal, for example Ni, Au and Pd, or an alloy comprising one of said metals. Separating channels are arranged between the individual contacts such that the contacts are electrically insulated from one another.
In this case the contact region of each card, said contact region including the contacts, hitherto has normally had the metallic color of the contacts themselves. In addition, for some time there has been the possibility of creating non-colored or single-colored images on the contact areas by means of metal etching.
FIG. 1 shows a schematic cross-sectional illustration of a construction/layer structure of a conventional single-colored coating of the contact region of a smart card module. In this case a metallic mirror layer 114, for example composed of chromium or high-grade steel, deposited on a surface 112 to be coated. Arranged on the metallic mirror layer 114 is a coloring layer 116 composed of indium tin oxide (ITO), which in turn can be overlaid with a metallic protective layer 118, for example composed of iron or gold. In this case, the color of the coloring layer 116 is dependent on the thickness of the coloring layer 116. To put it another way, the coloring layer 116 determines the optical impression, for example red or green or blue color depending on the thickness of the coloring layer 116.
However when the smart cards having a conventional single-colored coating of the contact region of the smart card module are used in everyday use, the gain in security on the basis of these single-colored images is very small.